Compound master cylinder



Jan. 1, 1952 A, B, SEPPMANN 2,580,850

COMPOUND MASTER CYLINDER 2 SHEETS-SHEET l Filed Aug. 17, 1946 55 44 ZfredB. m BY jep/2 ann am P www ifi'gs.

Jan- 1, 1952 A. B. SEPMANN 2,580,850

COMPOUND MASTER CYLINDER Filed Aug. 17, 1946 2 SHEETS- SHEET 2 82 J 58 INVENToR.

ilfed .Sepp/nanfa 745455 42M 7a fa Patented Jan. 1, 1952 UNITED STATES PATENT OFFICE COMPOUND MASTER CYLINDER Alfred B. Seppmann, Mankato, Minn.

Application August 17, 1946,' Serial No. 691,251

This invention relates to fluid pressure braking systems such as employed in automobiles.

y Particularly, the invention has reference to a compound master cylinder for producing atwophase operating'function.

The purpose of the two-phase feature is to rapidly take up slack in the brakes in the initial portion of the operation of the piston, by means of low pressure high-speed movement of lfluid, and on the final portion of the operation of the piston to apply high pressure movement of the fluid. Such master cylinders usually utilize two -pistons of diiferent diameter, arranged so that in the initial phase of the braking operation, the larger diameter piston applies force. In the'second phaseof the operation, a relief valve comes into play relieving the pressure on th'e fluid in thegcylinder having the larger diameter piston, whereby the smaller diameter piston is utilized for applying highpressure at a slower speed.

An object of the present invention is the'proe vision of a new arrangement of pistons in such a compound master cylinder, whereby the larger diameter piston telescopes over the smaller diameter piston.

Another object of the invention resides in the feature that the smaller diameter piston isflxed to a cap which closes the cylinder and'remains stationary, and the larger diametrvpistonv is `reciprocable in the cylinder and telescopes over the smaller diameter piston. An advantage resulting from this design is ease in assembling and disassembling the parts, and the elimination of constructional parts for closing the cylinder.

Animportant advantage in the present invention resides in a new andimproved relief valve for relieving the pressure on the fluid in the cylinder having the larger diameter piston at the beginning of the second phase of operation. The device includes a reservoir in communication with the large operating cylinder proper, and when the relief valve is opened fluid from the cylinder proper passes into the reservoir. Another important feature of the invention is that. the relief valve is arranged to permit reverse flow of fluid from the reservoir into the large operating cylinder, to enable the larger diameter piston to build up additional pressure by means of sudden and successive reciprocations in the braking operation. Y Another advantage of the invention resides in the arrangement of ports and passages in the relief valve so that when fluid' escapes therethrough it shielded frompassing outwardly 2 Claims. (Cl. Gil-54.6)

of the reservoir through vents which are usually provided in such cylinders.

Another advantage of the invention is the provision of a brass sleeve lining in the cylinder housing, inwhich the larger diameter piston operates.` In hydraulic systems there is usually a small quantity of moisture in the fluid which tends to accumulate in and rust the interior of the cylinder. The provision of such l a brass sleeve lining prevents rustfrom forming as. a result of such moisture. Another object of the invention resides in the cylinder for reciprocation of the piston and the fluid reservoir being formed integral, resulting in an economical structure.

A further object of the invention is the provision of a new and improved means for mounting a stop-light actuating switch on theqmaster cylinder.

vWith these and other objects in view, my invention consists in the construction, arrangement and combination of the various parts of 'my device whereby the objects contemplatedare at'- tained, as hereinafter more .fully set forth, pointed out in the claims and illustrated in the accompanying drawings, wherein: i

Fig. l is a semi-diagrammatic view of draulic braking system, including the master cylinder of my invention, showing the master cylinder in exaggerated size;

Fig. 2 is a top view of the master cylinder;

Fig. 3 is an end view, as viewed from .the left of Fig. 2;

Fig. 4 is a longitudinal sectional view, on an enlarged scale, taken on line 4--4 of Fig. 2;

Fig. 5 is a view similar to Fig. 4, showing the Areciprocable piston in extended position;

Fig. 6 is a vertical cross-section taken on line 6-6 of Fig. 5; i

Fig. 7 is an enlarged vertical sectional view of therelief valve; l

Fig. 8 is a horizontal sectional view taken on line 8 8 of Fig. 7; and K Fig. 9 is a sectional view of the retarding valve showing its positionduring back ow of lfluid from the brakes to the master cylinder. Y Y

Referring in detail to the drawings, vlFig. `1 shows a diagrammatic arrangement of `a braking system,r andthe compound master cylinderis indicated at I2, and a brake Vpedal I4 Vfor operating the cylinder. Connected to Vthe outlet i6 of the cylinder are conduits I8v leadingto vfluid motors 20. Actuation of the fluid motors expands the brake shoes 22 into engagement with brakedrums 24 in a'well-known manner. A,

The master cylinder is formed as a unitary casting having a, fluid reservoir 26 and a large operating cylinder 28. For purposes of identification the left end of the cylinder (Fig. 4) will be referred to as the rear end, and the right end the front end. At the rear end of the operating cylinder is a flange '38 for securing the master cylinder to a suitable mounting on the automobile. Outwardly of the flange 38 is a smaller flange or rib 32 over which may be secured a flexible covering for enclosing that end of the cylinder against the entrance of foreign matter. Both ends of the operating cylinder 28 are open in the formation of the article. The rear end of the cylinder has a reduced portion 34 and forward of the reduced portion 34 is an enlarged portion 36 extending to the front end thereof. A shoulder 36 is thus formed at the rear end of the enlarged portion 36. The open front end is closed by a cap 38 having threaded securement in that end of the cylinder. The cap 38 is provided with a central threaded bore 48, and a. central cavity 4| in its inner face.

The enlarged portion 36 of the operating cylinder 28 is provided with a movable brass sleeve 42.

A stationary piston 44 having a flange 46 is secured in the operating cylinder 28 with the flange 46 positioned adjacent the inner end of can 38, and the piston extends axially into the operating cylinder 28. Sealing means 48 is positioned on each side of thel flange 46, and the piston is retained in position by turning the cap 88 tight in the cylinder, and securing the flange 46 of the piston 44 between the cap and the adjacent end of the sleeve 42, and the other end ofthe sleeve abuts against the shoulder 35 and is held in position thereby, and the piston 44 is thereby held in position. The rear end of the piston 44 is provided with a flange 58 having a plurality of axial openings 52 spaced therearound. Rearward of the flange 58 is a reduced extension 54 having an annular recess 56 adjacent the rear face of the flange 58. Cup-shaped sealing means 58, is provided with a central opening for fitting in the annular recess 56. The sealing means 58 is adapted to Seat against the rear face of the flange 58 and seal the openings 52. A central bore 59 is formed in the piston 44, openinginto the cavity 4I in the end cap 38 at one end, and opening at the other end into the interior of a secondary cylinder, hereinafter described.

Operation of the master cylinder is effected by a. reciprocable piston 68, in the operating cylinder 28. The piston 68 is provided at its rear end with a cavity 62 for the reception of a rod 64 secured to the brake pedal I4. The front end of the piston 6071s hollowed, forming a secondary cylinder 66.

Surrounding the exterior of the piston 68, intermediate the ends thereof, is a flange 68 having an annular recess 18 formed therein. A cup-shaped sealing means |2 is fitted in the recess 18 and adapted to have sealing engagement directly with the brass sleeve lining 42 in the operating cylinder 28. Adjacent the rear end of the piston 68 is an annular recess 14, in which is positioned another cup-shaped sealing means 16 having sealing engagement with the reduced portion 34 of the operating cylinder.

A compression spring 'I8 is placed in the secondary cylinder 66 formed in the piston 60. This compression spring is biased between the inner end of the cylinder 66 and the rear end of the piston 44, and biases the reciprocable piston 68 to the left as shown in Fig. 4, or to its retracted position. Surrounding the reciprocable piston 68 is another compression spring 18, which is biased between the flange 68 on the reciprocable piston, and the flange 46 on the stationary piston 44. This spring also urges the reciprocable piston to retracted position. A plurality of openings 88 are formed in the reciprocable piston 68 at spaced intervals therearound, and are so positioned that whenthe piston 60 is in its retracted position as shown in Fig. 4, they communicate between the interior of the piston 68 and the operating cylinder 28.

Positioned in the cavity 4| in the inner face of the cap 38 is a retarding valve indicated in its entirety by the numeral 8|. The retarding valve 8| includes a, metal cup 82 having a flange 84 around its marginal edge. A compression spring 86 is biased between the flange 84 and the outer end of the piston 44. The cup 82 is provided with a plurality of openings 88 in its end surface. A flexible disc 88, such as rubber or leather, is secured to the inner surface of the cup 82 by means of a rivet 92, and is adapted to overlap and close the openings 88. A second disc 94 is positioned between the flange 84 of the cup 82 and the shoulder constituting the bottom of the cavity 4I of the cap 38. This disc 94 is provided with a central opening 96.

Threaded into the central bore 48 of the cap 38 is a plug 88. The plug 98 has a central bore I 88 therethrough, in alignment with the opening 96, and terminating forwardly in an enlarged bore |82 for connection to the outlet |6 of the master i, cylinder which leads to the fluid braking system.

Formed toward the front of the plug 98 is an enlarged shoulder |84, and outwardly of the shoulder I 84 is a further enlarged head in the nature of a nut as indicated at |86. A stop-light switch, indicated generally at |88, is provided with a ring ||0 surrounding the plug 98 and bearing on the shoulder |84. This ring forms an annular recess ||2 around the reduced portion of the plug 98. Sealing means I I4 is interposed between the ring ||8 and the front surface of the cap 38, and between the ring and the head |86. By tightening the plug in the opening 40 of the cap, the ring I I8 and the stop-light switch are secured tightly in position. A bore I I6 communicates between the central bore |88 of the plug and the annular recessA I|2. A similar bore ||8 is formed radially through the ring ||8 and communicates between the annular recess |I2 and the interior of the stop-light switch |88.

Formed in lthe wall between the reservoir 26 and the large operating cylinder 28 is a large port |28 positioned adjacent the shoulder 35. A short distance rearwardly of the port |28 is a smaller port |22 in the same wall. Toward the rear ofthe reservoir is an enlarged threaded opening |24 communicating with the interior of the operating cylinder 28 for the insertion of a relief valve mechanism |26. The brass sleeve lining 42 is formed with appropriate openings to register with ports and openings |28, |22 and |24. The valve |26 includes a chambered body |28 having a reduced lower end |38 for threading into the opening |24. A port |32 is formed centrally in the reduced portion |384 and communicates between the operating cylinder 28 and the interior of the chambered body |28. Surrounding the port |32 on the interior .surface of the chambered body is a raised shoulder |34. Formed in the side wall of the chambered body |28 above the raised shoulder |34 are a plurality A valve closure member |38 is positioned in the chambered body |28 and provided on its bottom with a resilient sealing means |40 for engagement with the upper surface of the raised shoulderv |34 for sealing the port |32. The chambered body |28 is formed with its top open, which is closed by a plug |42 threaded in an enlarged portion in the upper end of the chambered body. At the bottom of such enlarged portion are a plurality of radial ports |44 cornmunicating between the interior of the chambered body, above the valvev member |38, and the reservoir. The lower surface of the threaded plug |42 may be provided with openings |46 so spaced aroundits periphery that in any position of the plug |42 at least some of the ports |44 will be open and free for the passage of fluid therethrough. Biased between the plug |42 and the valve closure member |38 is a compression spring |48.

Through the bottom of the chambered body |28 are a plurality of passages |50 extending radially into the chambered body, and then downwardly and opening at the lower surface of the reduced portion |30 of the relief valve. These passages |50 communicate between the reservoir 26 and the operating cylinder 28, and by-pass the interior of the chambered body |28.

The lower surface of the reduced portion of the relief valve is concave in formation, and is provided with a downwardly extending projection |52 having an annular recess |54 positioned adjacent the concave lower surface. A flexible disc |56, such as rubber or leather, having a centralopening isplaced in the annular recess ,|54 and lies against the concave lower surface of the relief valve to normally close the ports formed by the passages |50.

Above the relief valve |26 is a threaded opening |58 for the insertion of the relief valve. This opening |58 is closed by a plug |60. .The plug |60 is hollowed-out as shown at |62-and at the top of the hollowed portion |62 is one or` more horizontal vents |64. The lower end of the hollowed portion |62 is substantially closed by a disc |66 having a central opening. The disc |66 thus prevents oil from passing out through the vent |64, such as might occur upon sudden return movement of the large piston 60, in its cylinder, while at all times insuring proper opening for the passage of atmosphere.

An opening |68 is formed in the top surface of the reservoir over the ports |20 and |22, to provide access for forming the ports |20 and |22, and is closed by a snap metal disc |10.

Operation Figure 4 shows the reciprocable piston 60 in retracted position. On the initial forward movement of the piston 60, it is moved to the right by the brake pedal. The port |22 is sealed-off by the sealing means 12, and the ports 80 are sealed off by the sealing means 58. The spring |48 has sufficient compression to normally retain the relief valve |20 closed, and fluid in the operating cylinder 28 builds up in pressure and passes through the ports 52 into the interior of the reciprocable piston 68, and is forced through the bore in the stationary piston 44 into the cavity 4| in the cap 38. Pressure built up here actuates the flexible disc 90, of the Iretarding valve assembly and opens the ports 88 in the retarding valve 8| 'permitting the fluid to pass on into the braking system (see Figr). The effect of this initial movement is to produce low pressure by the reciprocable piston 60 at a rate determined by the reduction in volume of the operating cylinder v28, ahead of the piston 60. v

After the slack hasbeen taken out of the braking system and the brake shoes are in engagement with the brake drums, back pressure is developed in the forward portion of the cylinder 28, to overcome the compression in the spring |48 in the relief valve |26. At this point, the valve closure member |38 is raised, relieving the pressure built up in the operating cylinder 28. The passage of fluid through the port |32 vin the relief valve |28 raises the valve closure member |38 above the radial portsv |36 and permits uid to pass into the reservoir, as indicated in Fig. 5.

Bythe reduction of pressure in the operating cylinderV 28 the fluid ceases to flow through the ports 52 in the stationaryV piston 44 and the result of further movement of the reciprocable piston 60 causes the fluid in the interior of the piston 60 to'be forced into the braking system. Y By this action, thespeed of the low of fluid into the braking system is reduced, but the pressure exerted thereon is greatly increased and thusprovided adequate, rapid, final braking action.

To build up greater pressure in the operating cylinder 28 the brake pedal may be actuated two or three times in quick succession. As the piston 60 moves quickly to retracted position, the spring 86 in the retarding valve 8| retains the retarding valve closed, preventing backflow of fluid from the braking system. Itis only after a slight lapse of time that the iiuid from the braking system reverses through the retarding valve 8| and will not reverse when the piston 60 is reciprocated quickly. Y r f Also, as the piston 60 retracts, the flexibleI disc |56 on the reliefvalve permits fluid fromthe reservoir to pass through the passages |50 into the operating cylinder 28. This additional quantity of fluid in the operatingk cylinder 28 enables in, creased pressure to be exerted. The plurality of passages |50 in the relief valve |26 permits sudden ow of fluid fromvthe reservoir 26 into the operating cylinder 28, when the piston 60 moves to retracted position, which causes a partial vacuum in the operating cylinder and opening of the valve |52. Thisaction is particularly effective when the brake pedal is actuated several times quickly.

After pressure is released from the brake pedal, the back pressure of fluid from the braking system opens the retarding valve 8|, as shown in Fig. 9, and ows into the interior of the master cylinder again. When the piston 60 moves to retracted position the ports are again in communication between the interior of the piston 60 and the operating cylinder 28, and the fluid on backflow from the brakes passes therethrough into the cylinder 28.

The radial ports |44 above the valve closure member |38 provide vent means above the valve closure member |38 to permit raising of the valve closure member.

The horizontal disposition of the ports |36 assures that any fluid passing therethrough travels horizontally and prevents loss of fluid out of the reservoir, as would occur if these vents were placed vertically, as they are in most old type devices.

The stop-light switch |08 may be rotated to any position around the plug 98, and in all positions thereof, the bore IIS is in communication with the annular recess I I2.

The reduced area of the upraised shoulder |34, and the resilient sealing means |40 on the valve closure member |38, insures that tight sealing engagement will be effected for closing the central bore |32. Grit or sand will not prevent tight sealing of this bore, as it would in the case of metal-to-metal contact.

While I have herein shown a particular embodiment of my invention, it will be understood of course that I do not wish to be limited thereto since many modifications may be made, and I therefore contemplate by the claims appended hereto to cover any such modications or substitutionsof equivalents as fall within the true spirit and scope of my invention.

I claim:

1. In a compound master cylinder for a braking system, a fluid reservoir, a cylinder, a hollow piston reciprocable in the cylinder and having a retracted position at one end of the cylinder, a stationary piston secured in the other end of said cylinder and co-axially aligned with the hollow piston, the hollow piston being adapted to telescope over the stationary piston, the hollow piston having formed therein openings communicating between the interior of the hollow piston and the cylinder when 'the hollow piston is in retracted position, said openings in the hollow piston being closed when the hollow piston is extended, the

stationary piston having a cupped sealing means cooperating with the interior of the hollow piston,

mentioned cylinder to open communication between it and the reservoir, said stationary piston having a bore communicating between the interior of the hollow piston and the braking system and a retarding valve between said bore and the braking system.

2. In a compound master cylinder for a braking system, a reservoir, a cylinder communicating with said reservoir, said cylinder being formed open at both ends and having a shoulder in one of said ends. a cap closing said last mentioned end of said cylinder, a stationary piston having a ange secured between said cap and said shoulder, said stationary piston extending into said cylinder, a hollow piston reciprocable in said cyl inder having a retracted position at one end of the cylinder and adapted to telescope over said stationary piston, said stationary piston having sealing means cooperating with the interior o! said hollow piston, there being openings communicating with the interior of said hollow piston and said cylinder when said hollow piston is in retracted position, said stationary piston having openings therethrough for the passage of fluid in one direction past said sealing means, said stationary piston having a bore communicating between the interior of said hollow piston and said cap, said cap in turn communicating with the braking system, a retarding valve in said cap to permit ready ow of brake fluid to the braking system and retard reverse now therefrom, and spring biased valve means for permittingpassage of uid from said cylinder into the reservoir when a predetermined pressure is attained in the cylinder.

ALFRED B. SEPPMANN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date Re. 16,761 Loughead Oct. 4, 1927 1,709,150 Pieper Apr.'16, 1929 2,050,702 Jackson Aug. 1l, 1936 2,166,742 Lambert July 18, 1939 2,208,575 Frank July 23, 1940 2,248,426 Fowler July 8, 1941 2,277,292 Bowen Mar. 24, 1942 2,291,056 Pallady July 28, 1942 2,349,416 Freeman May 23, 1944 2,374,235 Roy Apr, 24, 1945 2,384,186 Magrum et al Sept. 4, 1945 

